A simple suitable microfluidic devise for investigating the effect of shear stress on the stem cell differentiation to the chondrocyte cells

A simple suitable microfluidic devise for investigating the effect of shear stress on the stem cell differentiation to the chondrocyte cells
Hajar Moghadas,^1,*
1. Department of mechanical engineering, Gas and Petroleum Faculty, Yasouj University, 75918-74831, Iran
Introduction: Cartilage and joints disorders are very common among people [1]. Tissue engineering today provides a new solution for cartilage regeneration based on the use of a combination of cells, scaffolds, and biomolecules [2, 3] that needs a good number of the cellular source. The number of patient chondrocyte cells is not enough for transplant, and donors are usually scarce. On the other hand, stem cells of unlimited proliferation, simple culture, and chondrocyte differentiation can be considered as a suitable source for the production of chondrocyte cells [4]. The microfluidic devices provide the conditions of applying the chemical and mechanical stimuli to the cell differentiation[4] [5], [1] [7] . The differentiation of chondrocyte cells within the bioreactor under mechanical stimulation of compressive and shear forces has been investigated [8] and showed that shear stress alone reduces the process of the cell differentiation in that situation. However, from the mechanical point of view, the shear force is not uniform in that case, so it is not possible to properly assess the effect of the shear force on the cell differentiation. In the present work, a simple microchip is designed and fabricated to create a uniform shear force on the cells.
Methods: The mold of the microchip has been created by CNC on PMMA (Polymethyl methacrylate). The microchip has fabricated by molding method using polymeric PDMS (Polydimethylsiloxane). This microchip consists of a main channel with a rectangular cross-section. The length, width, and height of the main channel are 2 cm, 1 mm, and 500 µm, respectively. The cells will be cultured on the floor of the channel, and the culture medium passes through them to exerts shear forces on the cells. The microchip has been connected to a syringe micro-pump. The syringe micro-pump inserts the culture media into the microchannel with the controllable amount. The shear stress distribution on the cells in the microchip is modeled with the computational fluid dynamic simulation. The amount of shear stress has been controlled by the flow rate by the syringe micro-pump.
Results: It is shown that the shear stress distribution on the cells is almost uniform for a flow rate of 1 to 100 µl/min. The variation of the shear force on the cells embedded in the floor of the channel is plotted against the mass flow rate of the culture media on fig. For a flow rate of 1 to 100 µl/min the shear stress varied linearly from 0.0005436 to 0.05432 Pa. The amount of shear stress is controlled by the flow rate that can be adjusted by the syringe micro-pump.
Conclusion: The data show that the shear force on the floor of the microchannel is almost uniform. The amount of shear stress is easily controlled by the mass flow rate. This simple microchip proved the condition to investigate the effect of the pure shear stress on the differentiation of stem cells into chondrocyte cells. As the future work, we plan to culture the stem cell on the microchip and study the effect of shear force and chemical stimulation in the cell differentiation to the chondrocyte cells.
Keywords: Microfluidic, Chondrocyte cells, Stem cell differentiation, Mechanical stimulation